In processes for the production of semiconductor devices, for example, IC or LSI, fine fabrication is conducted by means of lithography using a photoresist composition. In recent years, as the degree of integration in integrated circuits increases, it has been requested to form an ultra fine pattern in the submicron region or the quarter micron region. With such a trend, an exposure wavelength tends to become shorter such as from g-line to i-line and further to a KrF excimer laser beam. Moreover, the development of lithography using an electron beam, an X ray or an EUV beam also proceeds at present in addition to the use of an excimer laser beam.
In particular, the electron beam lithography is regarded as the pattern formation technique of next generation or after the next generation, and the development of a positive resist having high sensitivity and high resolution has been desired. Particularly, the increase in sensitivity is a very important problem in order to shorten a wafer processing time. However, when high sensitivity is tried to pursue with respect to a positive resist for an electron beam, a problem arises in that preservation stability after exposure in vacuo (hereinafter referred to as in vacuo PED) deteriorates. Thus, development of resist that satisfies both requirements has been strongly required. The same problems are also present in lithography using an X ray or an EUV beam and thus it is desired to solve these problems.
As a resist suitable for lithographic process using an electron beam, an X ray or an EUV beam, a chemical amplification resist utilizing mainly an acid catalytic reaction is used in view of the increase in sensitivity. With respect to a positive resist, a chemical amplification composition containing as the main components, a polymer having a property of being insoluble or hardly soluble in an aqueous alkali solution and becoming soluble in the aqueous alkali solution upon the action of an acid (hereinafter also referred to as an acid decomposable resin) and an acid generating agent is effectively used.
With respect to a positive resist for an electron beam or an X ray, resist techniques for a KrF excimer laser have been mainly diverted and investigated. For instance, a resist composition containing a polymer wherein phenolic hydroxy groups of poly (p-hydroxystyrene) are fully or partially protected with tetrahydropyranyl groups is described in Patent Document 1 (JP-A-2-19847 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
Also, a resist composition containing a polymer wherein from 20 to 70% of phenolic hydroxy groups of poly (p-hydroxystyrene) are substituted with acetal groups is described in Patent Document 2 (JP-A-4-219757).
Further, it is described in Patent Document 3 (JP-A-9-319092) that a resin having an acetal group introduced is effective for reduction of standing wave.
Moreover, resins containing substituted acetal units are described in Patent Document 4 (JP-A-10-221854), Patent Document 5 (JP-A-11-305443) and Patent Document 6 (JP-A-2002-323768).
However, under the present situation, the techniques described above cannot simultaneously satisfy the high sensitivity, high resolution, good pattern profile and good in vacuo PED property. Particularly, the in vacuo PED property is a very important property in case of exposing in vacuo with an electron beam or an X ray. When the in vacuo PED property is poor, performances are remarkably changed between the initial stage of drawing and the final stage of drawing in case of drawing with an electron beam or an X ray. As a result, uniformity of line width in the drawing pattern is significantly injured and severe reduction of yield occurs.
Thus, according to the combination of conventionally known techniques, it is difficult to satisfy all of the high sensitivity, high resolution, good pattern profile and good in vacuo PED property under irradiation of an electron beam or an X ray. Therefore, it has been strongly desired to satisfy all of these properties.                Patent Document 1: JP-A-2-19847        Patent Document 2: JP-A-4-219757        Patent Document 3: JP-A-9-319092        Patent Document 4: JP-A-10-221854        Patent Document 5: JP-A-11-305443        Patent Document 6: JP-A-2002-323768        